Gear train



T. F. l. ToMLlNEs GEAR TRAIN Filed Jan. '7, 1946 June 27, 1950 .A TTORZVEY Patented June 27, 1950 Thomas F. I. Tomlne s, Rockville Centre,V N. Y.,

assignor to the United States. of America as represented by the Secretary of the Navy Application January 7, 1946,.-Serial'N0. 639,672

rThis invention relates to gear trains. Its object is to provide an improved mechanism for eliminating backlash in a speed-change drive train, andv more particularly in speed-reduction gearing.

ln accomplishing the above object, a speedreduction gearing unit is provided in addition to a primary drive train and is mounted for rotation cf its axis about the aXis of a gear in the primary drive train. A spring connected between the rotatable mounting and the stationary frame effects elimination of backlash in the primary drive train in a simple and effective manner.

The invention will be better understood from the following detailed disclosure and from the drawing, in which Fig. l is a plan View of a gear train,` showing a preferred embodiment of the invention; and

Fig. 2 is a latera-l section along the line- 2 2 in Fig. l.

A drive shaft lil is mounted rotatably in bushing i2, which is supported by frame plate I4. Pinion it, which is nXed on shaft Eil, drives gear t8, mounted rigidly on shaft 2li', which is mounted rotatably between frame plates I4 and I4. Also fixed rigidly to shaft 2t is a pinion 22 in mesh with gear 24, which is iiXed on driven shaft 26.

Said shaft 2t is mounted in a bearing 28 supported in frame plate I4'. Frame plates I4 and i4 are spaced from each other by four spacing studs 36 threaded into plate Ill, the studs acting to conne plate I4 through coaction` of nuts 34 with threaded portions 32 on the studs. Shafts it and 2t are arranged adjustably for accurate axial alignment by suitable design of the supports (not shown in detail) for bearings I2 and 28.

For the 'purpose cf preventing backlash in the above-described speed-reduction gearing, an additional gearing unit was provided in the prior art. Such structure included a primary gear drive train of the type shown as gears I6, I8, 22 and in the drawing and a secondary gear drive train comprisinfJ a gear and pinion mounted on a shaft xedly located, said gear meshing with pinion l and said pinion meshing with gear with a spring provided between said gear and said pinion to take up the backlash in the entire primary drive gear train. That arrangement was not only ditncult to make in that special construction of said gear, pinion the spring coupling required, but the device also required large components and was limited to use with only a spring of predetermined dimensions.

According to the present invention, the prior- 1 claim. (o1. 741-409) art arrangement for preventing backlash is replaced by an improved organization. Gear 3S and pinion 38 may now be constructed as exact duplicates of gear l2 and pinion 22, respectively, and are arranged to rotate as a unit. Gear 36 and pinion. 3G. are iixed rigidly to shaft tt, which is mounted rotatably in a cradle or subframe comprising plates 42 and. 42. This subframe is supported `on bearings I2 and 28 for arcuate motion about the axis along which shafts I3 and '28 are aligned. A pair of spacing` elements 44 are xed between plates 42 and 42. Tension spring 45 is arrangedbetween a spacer 44 and a spacing stud (Eig. 2.) to urge shaft 4i! toward arcuate travel aboutfthe-axisof shafts l0 and 276 in a clockwise direction, as shown, in Fig. 2. Since spring 46 is mountedV under such strong tension that the torque exerted is many times that needed to counter-balance the torque required to drive gear 24S, power is transmitted immediately when gear it? isrotatcd in a clockwise direction, and backlash in the primary gear drive train is prevented: Under-the action of spring lit, the teeth of pinion E2 and gear 24 are brought into the position showny and gear 35 and pinion 38 tend to revolve about shafts I0 and 26 in a clockwise direction having the eiect of tending to rotate shafts ID and. 2t.: at a one to one ratio. This brings the teeth of gear` 36 and pinion It into the position shown, so that pinion iS tends to rotate counterclockwise. Continuing to follow these rotations, it is seen that gear I8 and pinion 22 tend to rotate clockwise, and that gear 24 is urged in a counterclockwise direction. rlhis is the desired condition, as the teeth at the junction of gear 24 and pinion 38 are maintained by the spring 46 in the relationship shown. Contact between gear teeth all the way through the primary gear train to the driven gear is thus established and maintained for rotation of the driving pinion I6 in either direction, and backlash, play or lost motion between gear teeth is eliminated.

Further analyzing operation, it is to be observed that, when drive shaft Ill is at rest, said shaft I0 and consequently pinion it and. gear 24 are locked in position within the limits of backlash by gear train I6, I8, 22 and 24. The frame 42, 42', shaft di), gear 36 and pinion 38 being rotatable about coaxial shafts I0 and 2t, such rotation causes gear 36 and pinion 38 to roll along the circumferences of pinion I5 and gear 24 respectively. Such rolling action tends to cause less angular displacement of gear 35 than of pinion 38, due to the difference in diameter between said gear and said pinion, but such diierence in angular disfixed center has been established for shaft 40 in gear train I6, 36, 38 and 24, said center being so located as to prevent backlash in the gear train, and the speed reduction through the mechanism is obtained by simultaneous action of the two similar gear trains.

By integrally associating a shoulder portion and a set screw (not shown) with each of gears I8, 24 and 36, which are then rotatable on their shafts before tightening those screws, there may be `angular adjustment between shafts I0 and 26 and, at the same time, angular adjustment for subframe 42, 42 so that spring 46 may be made to exert any desirable degree of tension, within limits.

'It is evident that the provision of a subframe for supporting the backlash gearing simplifies the construction of the gearing and makes possible a reduction in the size of the components that would otherwise be necessary to enclose a suniciently strong spring in the prior art construction. Spring 46 may be any ordinary tension spring of suitable strength. It is replaceable readily upon breakage and for substitution by springs of differing strengths. It is evident that a compression spring between the subframe and the main frame might be arranged, as well as a torsion spring for that subframe, to some extent sacrioing the simplicity of the disclosed embodiment.A

.In a broader aspect of the invention, it will be found that spring-urged arcuate travel of a single gear in the backlash train about a driving or driven gear in a speed-change system will accomplish 'the result desired, so long as the drive train remains unbroken; that the driving and driven gears need not be coaxial. The gear trains coupling the driving and driven gears may be replaced by any broadly equivalent drive means, as by one 4 or more endless chains, and idler gears may be added when expedient. However, the invention is applied with particular advantage to the speedchange gear drive shown, and in the manner specified.

Various modifications and changes can be made in the subject device without departing from the scope of the invention.

I claim:

A gear train comprising a driving gear mounted rotatably in a frame, a driven gear mounted rotatably `in said frame in axial alignment with said driving gear, a, plurality of gears mounted in said frame and coupling said driving gear to said driven gear, a subframe mounted rotatably in said Mframe'in axial alignment with said driving and driven gears, a pair'of gears mounted fixedly on a common shaft, said shaft being carried rotatably in said subframe in axial parallelism with the` axes of said driving and driven gears, said pair of gears meshing with said driving and driven gears respectively, and resilient means connecting said frame and subframe to urge said subframe toward arcuate travel about the axis of said driving and driven gears.

THOMAS F. I. TOMLINES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

